In-medium ω\omega mass from the γ+Nb→π0γ+X\gamma + Nb \to \pi^{0}\gamma + X reaction

Data on the photoproduction of $\omega$ mesons on nuclei have been re-analyzed in a search for in-medium modifications. The data were taken with the Crystal Barrel(CB)/TAPS detector system at the ELSA accelerator facility in Bonn. First results from the analysis of the data set were published by D. Trnka et al. in Phys. Rev. Lett 94 (2005) 192303 \cite{david}, claiming a lowering of the $\omega$ mass in the nuclear medium by 14$$ at normal nuclear matter density. The extracted $\omega$ line shape was found to be sensitive to the background subtraction. For this reason a re-analysis of the same data set has been initiated and a new method has been developed to reduce the background and to determine the shape and absolute magnitude of the background directly from the data. Details of the re-analysis and of the background determination are described. The $\omega$ signal on the $Nb$ target, extracted in the re-analysis, does not show a deviation from the corresponding line shape on a $LH_2$ target, measured as reference. The earlier claim of an in-medium mass shift is thus not confirmed. The sensitivity of the $\omega$ line shape to different in-medium modification scenarios is discussed.Comment: 13 pages and 11 figures, submitted for publicatio

Photoproduction of Neutral Pions off Protons

Photoproduction of neutral pions has been studied with the CBELSA/TAPS detector in the reaction $\gamma p\to p\pi^0$ for photon energies between 0.85 and 2.50 GeV. The $\pi^0$ mesons are observed in their dominant neutral decay mode: $\pi^0\to\gamma\gamma$. For the first time, the differential cross sections cover the very forward region, $\theta_{\rm c.m.}<60^\circ$. A partial-wave analysis of these data within the Bonn-Gatchina framework observes the high-mass resonances $G_{17}$(2190), $D_{13}$(2080), and $D_{15}$(2070).Comment: 12 pages, 9 figures, minor modifications to PWA sectio

Photoproduction of η and η' mesons off protons

Total and differential cross sections for eta and eta(`)photoproduction off the proton have been determined with the CBELSA/TAPS detector for photon energies between 0.85 and 2.55 GeV. The eta mesons are detected in their two neutral decay modes, eta -<gamma gamma and eta -< 3 pi(0)-< 6 gamma, and for the first time, cover the full angular range in cos theta(c.m.) of the eta meson. These new eta photoproduction data are consistent with the earlier CB-ELSA results. The eta(`) mesons are observed in their neutral decay to pi(0)pi(0)eta -< 6 gamma and also extend the coverage in angular range

Photoproduction of π⁰ η on protons and the Δ (1700)D₃₃ -resonance

Total and differential cross-sections for the reaction γp → π&lt;sup&gt;0&lt;/sup&gt;ηp have been measured with the Crystal Ball/TAPS detector using the tagged photon facility at the MAMI C accelerator in Mainz. In the energy range E&lt;sub&gt;γ&lt;/sub&gt; = 0.95–1.4 GeV the reaction is dominated by the excitation and sequential decay of the Δ(1700)D&lt;sub&gt;33&lt;/sub&gt;-resonance. Angular distributions measured with high statistics allow us to determine the ratio of hadronic decay widths Γ&lt;sub&gt;ηΔ&lt;/sub&gt;/Γ&lt;sub&gt;πS11&lt;/sub&gt; and the ratio of the helicity amplitudes A&lt;sub&gt;3/2&lt;/sub&gt;/A&lt;sub&gt;1/2&lt;/sub&gt; for this resonance